Abstract:
The excavation support for the DL Tippin Water Treatment Plant project in Tampa, Florida, consisted of a two-tiered soil mix excavation support system with an excavation of up to 44 feet. Bottom seals of this magnitude are common in South Florida, but to our knowledge, this is one of the first bottom seals of its kind in Central Florida. This system was designed and installed with twin soil mix walls and a tied-down deep soil mix bottom seal so the excavation could occur in the dry without continuous dewatering. The upper tier of the excavation support system was tieback anchored into limestone since it was above the groundwater table where penetrations in the wall were permitted. The lower tier was below the groundwater table and was internally braced to avoid penetrations in the soil mix wall that would allow for groundwater to seep into the excavation.
The upper tier consisted of 34 tieback anchors that were drilled 70 to 85 feet and bonded into limestone. The limestone in the Tampa Bay region is notoriously karstic with voids and sinkholes being relatively common occurrences. The drilling of deep, high-capacity anchors in this geological condition is challenging and frequently results in excessively high grout takes and difficulty maintaining drilling circulation. The project required in-depth 3D modeling of the existing water treatment plant to coordinate the location of each anchor to avoid conflicting with existing utilities and structures.
Along the northern boundary of the excavation, an in-service 5 MG water tank was underpinned with jet grout. The water tank was especially sensitive to movement as it was to remain in-service during the full duration of the excavation. The water tank was instrumented with AMTS monitoring points which had automated readings and relayed movement data (x, y, and z) daily.